Ignitor-burner assembly



1966 H. T. CHILDREE 3,265,114

IGNITORBURNER ASSEMBLY Filed July 20, 1964 2 Sheets-Sheet 1 13 10l%/?M4A/ 0045,4 55,

INVENTOR.

United States Patent Office 3,2651 14 Patented August 9, 1956 3,265,114IGNITOR-BURNER ASSEMBLY Herman T. Childree, Cason, Tex., assignor toGeneral Dynamics Corporation, Pomona, Calih, a corporation of DelawareFiled July 20, 1964, Ser. No. 383,602 11 Claims. (Cl. 158-.-123) Thisinvention relates to burners, particularly to pilot ignitor-burners, andmore particularly to natural gas pilot ignitor burners which have theability to operate under adverse conditions.

One of the problems that has always confronted users of gas burners isbackfire. A backfire occurs when the rate of flame propagation exceedsthe velocity of the combustible gas mixture issuing from the burner.Another problem is so-called flame out or flame blow away. When thevelocity of the stream of combustible gas mixture issuing from theburner exceeds the rate of burning of the gas mixture, in whatever stateof dilution has been caused by the surrounding air, the flame recedes orflows away from the burner orifice and is usually extinguishedaltogether. The :burner flame remains stationary or sealed at thedischarge orifice of the burner, or a very small distance from it, onlywhen the velocity of the stream of combustible gas mixture issuing fromthe orifice is substantially equal to the rate of burning of the gas inthe stream.

Heretofore, but without full success, many attempts have been made todevelop a pilot ignitor-burner that would eflectively operate underadverse conditions. The basic design and operation of these prior artdevices depends on the mixing of air and gas in a suitable mixingchamber with an exit whose purpose is to direct the airfuel mixture to.a point at which it is discharged in the vicinity of a high voltagespark.

Several disadvantages are inherent in the prior art devices anddeleterious eflects result there-from. The maximum and minimum air-fuelmixtures of gas and air which can be ignited by a low intensity highvoltage spark are narrow. Therefore, it is necessary that the amount ofgas and air be closely controlled so that the air-fuel mixture that isdischarged in the vicinity of the spark plug is ignitable. In most casesin the prior art there are no provisions made to 'hold the flame at aspecific point. There are some devices whi h depend upon a divergingexit that permits the air-fuel mixture to establish a flame front at themost acceptable condition for sustained burn.- ing. In either case, anupset or change in pressure at the exit will, in most instances, cause aflame out. Any change in the supply pressures of gas and air willcorrespondingly change the air-fuel mixture. It has been noted thatvariations of as little as one-half pound in gas pressure will result inno ignition or a flame out. Variations in air pressure will produce thesame undesirable results.

The flame sensing installations on most of these basic devices consistof a high temperature metal rod that is positioned at a point which willsense the presence of the flame and initiate a signal or indication. Onsome prior art devices the flame rod is exposed to the flame at such apoint which will permit the flame rod to droop or sag and ground out.The prior devices produce a flame temperature that ranges from 1200degrees F. to 1500 degrees F. Observations show that the flame in mostoperating conditions is detached or blown away from the end of theseignitor-burners and is very easily blown out.

This invention provides an ignitor-burner assembly capable of operationunder a very Wide range of pressures and environmental conditions.

Therefore, it is an object of this invention to provide anignitor-burner assembly.

A further object of the invention is to provide a gas pilotignitor-burner assembly.

A still further object of the invention is to provide a gas pilotignitor-burner having the ability to operate under adverse conditions.

Another object of the invention is to provide a pilot ignitor-burnercapable of operation under a very wide range of pressures andenvironmental conditions.

Another object of the invention is to provide an ignitor assembly thatproduces a homogeneous mixture of air and gas by internal supersonicnozzle principle turbulence which results in a high velocity, hightemperature flame which is immune to most external variations.

Another object of the invention is to provide an ignitor assembly thatresults in the proper mixing of the gases by internal turbulence in theevent of low velocity or low pressure requirements.

Another object of the invention is to provide an ignitor assembly thatcontains a turbulating method that provides the necessary turbulence tohold the flame within the combustor section.

Another object of the invention is to provide an ignitorburner whichutilizes an ignition device and a flame sensing device. 1

Another object of the invention is to provide a burner assembly having aflame sensor positioned in a relatively low temperature area whichpermits the presence of a flame which is sensed by the control unit.

Other objects of the invention, not specifically set forth above, willbecome readily apparent from the following description and accompanyingdrawings wherein:

FIG. 1 is a view of one embodiment of the invention with portionscut-away to illustrate the internal elements;

FIG. 2 is a cross-sectional view of the FIG. 1 device taken on the line22 of FIG. 1;

FIG. 3 is a schematic view of the gas and air mixing of the FIG. 1device;

FIG. 4 is a perspective view of another embodiment of the invention;

FIG. 4a is an end view of the FIG. 4 embodiment;

FIG. 5 is a view partially in cross section of a combustion unitincorporating the invention; and

FIG. 6 is a schematic View showing the control system of the FIG. 5unit.

This invention is directed to an ignitor-burner which incorporates meansto mix air and gas in such a manner as to produce a high velocity, hightemperature flame which is immune to most environmental variations. Moreparticularly, the device comprises a conventional flame rod unit and aburner assembly comprising a pair of manifolds, one for air and theother for natural gas; a plurality of tubular elements; a high voltageelectrode; a spark bafiie; combustor grid; and various casings andinsulating elements. The ignitor assembly and the flame rod may bemounted adjacent to or concentric with each other with terminal portionsthereof extending through bores provided in a multiple-apertured flameholding or turbulator plate. The tubular elements are positioned in anannular arrangement surrounding the spark plug casipg, the terminalportion of which functions as a negative electrode for the abovementioned electrode, and adjacent this location is mounted the sparkbaffle. Alternative tubes of said annular arrangement are adapted toconvey the air and gas respectively. The flow emitting from the airtubes may or may not be supersonic, while the flow emitting from the gastubes is subsonic. Due to the particular arrangement of the tubes thereexists a supersonic jet of air on each side of a subsonic jet of gas,which results in a homogeneous mixture thereof. Due to the inability ofnatural gas, for example, to maintain a flame if its velocity is high,the flow of the result- 3 ing mixture is turbulated or deceleratedbefore reaching the spark gap by the above mentioned baflle andcombustor grid.

Instructions issued by the manufacturers of natural gas burnerspertaining to the maintenance of the natural gas pilots make a point instressing the importance of the flame rodcircuit. In most cases theirinstructions state that the flame rod should be removed and cleaned. Insome cases the flame rod needs to be replaced due to foreign materialbeing imbedded in the surface of the insulator, either at the end whichhas been subjected to the flame or at the connector end which may becontaminated by atmospheric conditions. There have been someimprovements in the type of ceramic material used and the method ofprotecting the connector point but the major problems in the flame rodassembly of the prior art devices still exist. These problems are veryapparent to those who have the responsibility of maintaining natural gaspilot systems. The inability of the flame rod in the prior art devicesto supply satisfactory results was the main reason why the infra-red andthe ultra-violet systems have been developed and by using these types offlame detection, the problem of the flame rod has been eliminatedalthough the overall cost of the system has been increased.

The ignitorburner assembly of this invention utilizes a conventionalflame rod assembly and sensing control unit. One unique feature of thisinvention is the placement of the flame rod. As the homogeneous mixtureof gas and air exhausts through the flame holder or combustor grid andignites, a relatively low temperature area is established in and aroundthe flame rod end creating the presence of a flame which is sensed bythe control unit. This flame rod of the sensor unit will remainrelatively cool.

Referring now to the drawings, the ignitor-burner assembly as shown inFIGS. 1 and 2 comprises a housing 10, an ignitor unit generallyindicated at 12, a flame rod unit indicated generally at 13, and acombustor grid or turbulator plate 14 operatively positioned in housing10.

Ignitor unit 12, in this embodiment, comprises a housing 15 defining anair manifold 16 and a gas manifold 17; an inlet passage 18 connectingair manifold 16 to an air supply source (see FIG. 6); an inlet passage19 connecting gas manifold 17 to a gas supply source; an electrodeassembly generally indicated at 20; air and gas conduits 21 and 22,respectively, positioned around a separator 25 which is located aroundan electrode assembly 20, conduits or tubes 21 and 22 being operativelyattached to their respective manifolds. A combustor grid baflle plate 23is positioned around said separator 25, and means such as nut 24 forattaching the ignitor unit housing 15 within an aperture in housing isplaced around a portion of housing 15. As shown in FIG. 2, gas conduits22 are positioned intermediate air conduits 21 except in applicationswhere housing portion is of such diameter as to require an odd number ofconduits due to the external diameter of separator 25, the internaldiameter of the housing 15, and the external diameter of the conduits,as in this embodiment, wherein an extra air conduit 21 is positionedbetween gas conduits 22. Electrode assembly consists of a casing 26operatively located within separator 25, and a positive electrode 27 isinsulated at 26 from casing 26, casing 26 terminating in a pair ofpoints 28 (only one shown) which serve as the negative electrode (seeFIG. 1). The insulator material should be of the type which exhibits agood dielectric constant at high temperatures, good mechanical strength,and good thermal shock capabilities. Housing portion 15 terminates atpredetermined distance from bafl'le plate 23 to provide homogeneousmixture of the air and gas flowing from conduits 21 and 22 which will bepresently described.

Flame rod unit 13 comprises a casing 29 and a flame sensor rod orelectrode 30 insulated from casing 29 by material having the samequalities as set forth above with respect to the insulator material ofthe ignitor unit 12, and means such as retainer nut 31 for holdingcasing 29 with respect to housing 10. The material used for the rod 30should exhibit good high temperature capabilities. The action of flamerod unit 13 is identical with the present state of art in sensing thepresence of a flame. However, the manner of installation of the flamerod unit 13 in housing 10 greatly reduces the existing problemspresently encountered in flame sensing. The main problem with the flamerod installation of the prior art assemblies is not the flame roditself, but arises from the necessity of using this type of sensingwhere an ineflicient pilot and/or burner is used that results in acondition which causes carbon or other foreign substance to build up onthe flame rod creating a low resistance to ground. Various prior knownpilots require that the flame rod be inserted deep into the flame, thusif rough burning occurs, the insulation of the flame rod unit will breakor the rod itself becomes hot enough to permit it to bend and touch themetal housing, shorting out the flame sensing circuit. The flame rodunit 13, when utilized as illustrated and described herein, does notsuffer the same effects as the prior art approaches because (1) it is anintegral part of the pilot system and is not mounted separate from thepilot, thus requiring only one mounting hole, (2) it is mechanicallystrong and securely mounted, (3) it is not subjected to any hightemperature flame, (4) it is installed in a manner so that it cannotbecome contaminated with carbon build-up or any foreign matter, and (5)it has a connection to the flame sensing circuit which is protected inthe same manner as the spark connection of unit 12 and results in acompact unit.

Combustor grid 14 is provided with a plurality of apertures extendingtherethrough as indicated by the dotted lines in FIG. 1 to allow themixture of air and gas to flow from mixing chamber 32 to combustion zone33 where the mixture is ignited by the electrode assembly 20 whichextends through a passageway in grid 14 and into combustion zone 33 apredetermined distance. Flame rod unit 13 is mounted in a passageway ingrid 14 so that flame sensor rod 30 extends a predetermined distanceinto combustion zone 33. The apertures in combustion grid 14, throughwhich the air and gas mixture passes, may have various configurations,for example, straight or angled holes, straight or angled slots whichextend from the center outwardly, or horizontal or vertical slots. Thespecific aperture configuration is dependent on the flow patterndesired.

Referring now to FIGS. 1-3, the basic operation of the invention is asfollows. Pressurized air is supplied to air manifold 16 through inlet18. This pressurized air is directed from manifold 16 through conduitsor tubes 21 and discharges from these conduits into the mixing chamber32. If the pressure is great enough, conduits 21 will choke, resultingin a high velocity flow of air. Gas under pressure is supplied throughinlet 19 to manifold 17, an orifice 34 may be positioned in gas inletpassage 19 if desired. This pressurized gas is directed from manifoldthrough the conduits or tubes 22 and discharged into the mixing chamber32.. As described above, and shown in FIGS. 2 and 3, conduits 21 and 22are so positioned that there is a gas flow each side of a high velocityair flow. This high velocity air tends to pull the gas discharging fromconduits 22 along with it as it enters the mixing zone 32. This isproduced by the aspiration effect of the high velocity air dischargingfrom conduits 21. The remaining gas flow is forced by the manifoldpressure into the very turbulent area at the point where the highvelocity air expands or becomes subsonic. In this extremely turbulentarea a homogeneous mixture is produced. This resulting mixture or aportion thereof impacts against baffle 23 which prevents the mixturefrom flowing into combustor grid 14 and slows the flow of the mixture toa low velocity. Baflle 23 directs the mixture or changes its fiowdirection thus providing more turbulence within mixing chamber 32 thusassisting in providing a complete homogeneous mixture of the gas andair. As the flow of air and gas continues from conduits 21 and 22, thestatic pressure increases slightly in the mixing chamber 32 behindcombustor grid 14, thereby causing it to flow through the apertures ingrid 14 into combustion zone 33. As this homogeneous mixture reaches thearea within zone 33 of ignitor assembly it is at a low velocity andeasily ignited by the spark across electrodes 27 and 28. The effectivearea of the cornbustion grid 14 is such that the resulting flame isslightly detached from the surface of the grid which keeps theelectrodes 27 and 28 and combustor grid 14 very cool and provides a verylong electrode life. Theilame within combustion zone 33 causes the flamerod 30 to operate in an identical manner as the flame rod units of thepresent state of the art. Note that the flame rod 30 does notnecessarily extend into the high temperature flame within zone 33 anddue to the efficient mixing and ignition of the ignitor unit 12, theflame is clean and does not deposit any foreign substance on the sensingportion of flame rod 30 which is within combustion zone 33, thusproviding trouble-free operation of flame rod unit 13.

Referring now to FIGS. 4 and 4a, the ignitor unit has been modified toincorporate the flame rod sensor and comprises essentially all of theelements of the FIG. 1 ignitor unit 12 except the center electrode 27functions both as the positive electrode and as the flame sensor rod andis extended further into combustion zone 33. Only the discharge andignition end of the unit has been shown in that the external electricalconnections are described hereinafter in the description of FIG. 6. Asshown in FIG. 4, the modified ignitor unit consists of housing 15'having air and gas conduits 21 and 22 discharging therefrom againstcombustor grid baflle plate 23' which is mounted on electrode casing 26as in the FIGS. 1 and 2 embodiment. Combustor grid 14 is provided with aplurality of apertures 35 which function to transfer the air and gasmixture to the combustion zone as described above. However, grid 14' isprovided with a central passage 36 through which the modified ignitorunit extends. As in the FIG. 1 embodiment, the end of electrode casing26 is pointed to define the negative electrodes 28' as shown in FIG. 40.Also, as in the FIG. 1 embodiment, the electrode 27' is separated forthe pair of electrodes 28 by insulator material indicated at 26". Theadvantages of the FIG. 4 device are in compactness wherein the overallsize of the ignitor-burner assembly can be reduced to approximately 75percent of that of the FIG. 1 embodiment.

The operation of the FIG. 4 modification is identical to the previousdescription of the FIG. 1 device except that the control system has atime delay and transfer relay to provide switching of the electrode 27'from flame sense to spark sense to flame sense, the details of thecontrol system being presently described.

The type of material used in the FIGS. 1 and 4 embodiments is dependenton the particular application thereof but should have a thermalexpansion coeflicient near that of the insulator material utilized inthe ignitor and flame rod units.

Referring now to FIG. 5, the ignitor-burner assembly described above andindicated generally at 40 is mounted in a burner generally indicated at41 which comp-rises a mixing and combustion assembly 42, a coolingsection 43, and an exit nozzle section 44.

Mixing and combustion assembly 42 comprises a housing 45 having platesor partitions 46 and 47 defining a gas manifold 48, an air manifold 49,and a combustion chamber 50. Gas is supplied to manifold 48 throughinlet passageway 51 from a source (see FIG. 6), while air is supplied tomanifold 49 through inlet passageway 52 from a source such as a blowershown in FIG. 6.

Housing 45 is provided with a central passageway 53 within which theignitor-burner assembly 40 is operatively positioned. Gas manifold 48 isprovided with a plurality of tubes 54 (two being shown) mounted inpartition 46 each tube 54 extending approximately /3 of the way throughan associated mixing tube 55 positioned in air manifold 49, attached topartition 47, and discharging into combustion chamber 50, there being anair tube 55 for each gas tube 54. A semi-swirl or turbulator plate 56 ispositioned in combustion chamber 50 adjacent the partition 47. Partition47 is provided with a plurality of apertures 57 through which air frommanifold 49 passes into the cooling section 43 which consists of ashroud 58 having a flanged portion 59 which is attached to a flangedportion 60 of housing 45 by means such as bolts 61, shroud 58 definingan annular air passage or cooling annulus 62 around the wall 63 ofcombustion chamber 553 for cooling thereof by air flowing from manifold49. The downstream end of shroud 58 is provided with a flange 64 whichis attached by means such as bolts 65 to a flanged portion 66 of exitnozzle section 44.

The basic operation of the FIG. 5 burner assembly is extremely simple.There can be any number of air tubes 55 and corresponding number of gastubes 54 placed equally around a circumference within partition or frontplate 47 to provide adequate mixing of the air and gas flowing intocombustion chamber 50. Pressurized air is supplied to manifold 49through inlet 2. Manifold 49 is pressurized and air flow is establishedthrough the mixing tubes 55 and the apertures 57 connected to the cool:ing annulus 62. The former air flow enters the combustion zone ofchamber 50 and continues down the combustor and exhausts through theexit nozzle 44. The air flow from apertures 57 flows down the coolingannulus 62 and exhausts through the exit nozzle 44. Gas under pressureis supplied through inlet 51 to manifold 43.

The manifold 48 is pressurized and gas flow is established through thegas tubes 54. The gas is discharged into the turbulent air streamflowing through and from mixing tube 55 and the mixture is dischargedinto the combustion chamber 59. At this point the gas and air mixturecomes in direct contact with the pilot flame generated by ignitor-burnerassembly 40 which is easily ignited. The combustion takes placeprimarily around the barrel of assembly 40. The semi-swirl or turbulatorplate 56 creates further turbulence at higher flows and holds the flamein this area by turbulence only. The combustion continues down thecombustion section 43 until it exhausts from the exist nozzle section44.

The cooling air may be injected into the cooling annulus 62 in analternate method by using a separate air inlet which may be directlyconnected between the air supply source and cooling annulus 62. Thisalternate method would eliminate the cooling air apertures 57 inpartition 47 and would require a balancing valve mechanism to controlthe air flowing to the annulus 62.

Referring now to FIG. 6, the control set-up for the FIG. 5 assemblycomprises an air supply source such as blower 68 which supplies air tothe ignitor-burner assembly 40 through conduit 69 and to the airmanifold 49 of the burner assembly through a conduit 70 having amodulating valve 71 positioned therein to control the supply of airtherethrough. Gas under pressure from a source as indicated by legend isdirected into a supply line 72 having a shut-off cook or valve 73. Aconduit assembly 74 interconnects valve 73 with the gas manifold 48 ofthe burner assembly. Positioned in conduit assembly 74 are a safetyshutoff valve 75, a service governor 76, and a modulating valve 77. Aconduit assembly 78 is connected to conduit assembly 74 between shutoffvalve 73 and safety valve and directs gas to the igniter-burner assembly40. A pilot regulator 79 and a solenoid valve 80 are positioned inconduit assembly 78. A valve controller mechanism 81 is mounted onmodulating valve 77 and controls modulating valves 71 and 77.

Controller mechanism 81 is operatively connected to a temperaturecontrol unit 82 via a valve control connection 83, while safety valve 75and solenoid valve 80 are operatively connected to a pilot control unit84 via a safety valve control connection 85 and a pilot gas controlconnection 86. Temperature control unit 82 is electrically connected toa power source 87 and to a thermocouple indicated by legend, while pilotcontrol unit 84 is electrically connected to power source 87, a startswitch 88 and a transfer unit 89.

The pilot control unit 84 is a conventional unit that is generally usedwith a burner setup, the details thereof being deemed unnecessary sinceit is not part of this invention. The unit will sense the flame byeither a flame rod, such as rod 39 of FIG. 1, or a photo-cell (notshown) through a flame sense Wire 98. Unit 84 is a self-contained unitthat attempts to light the pilot 4%) for a length of time and if a flameis not sensed, the unit will lock itself out and will need to bemanually reset. There can be no main gas flow signal to supply gas tomanifold 48 unless a flame is sensed.

The temperature control unit 82 is also a conventional unit, theoperation thereof being such that lit positions the valve controllermechanism 81 with respect to the temperature set point. The air and gasmodulating valves 71 and 77 are linked to controller 81 and the amountthat these valves are opened depends on the position of the controllinkage of controller 81. When properly adjusted, a constant air/fuelratio is obtained in the mixing and combustion section 42 of the burnerassembly over the entire .range of firing.

The transfer unit 89 consists of a time delay unit (TD) and a relay(R1). A high voltage transformer (T1) may be part of this unit, asshown, or mounted externally. If the ignitor-burner assembly 40 is ofthe FIG. 1 embodiment, which contains separate spark and flame rodunits, the transfer unit 89 will not be required; thus the flame sensewire 90 would be connected directly between the pilot control unit 84and the ignitor-burner assembly 40.

Where the ignitor-burner assembly 40 is of the FIG. 4 embodiment theoperation sequence of the FIG. burner assembly is illustrated in FIG. 6as follows:

(1) Blower 68 is placed into operation.

(2) Main gas cock 73 is opened.

(3) Temperature control unit 82 and pilot control unit 84 are turned on.

(4) The required temperature control point (not shown) is set on thetemperature control unit 82.

(5) After a suitable time has elapsed to insure that the control units82 and 84 have warmed up, the start switch 88 is actuated.

(6) Actuation of start switch 88 sends a signal to pilot gas solenoidvalve 80 to direct gas to assembly 40. (7) Simultaneous with item 6,power is applied to transfer unit 89. This voltage appears across thetime delay (TD) and the relay (R1). TD starts its delay immediately.Also R1 energizes immediately operating its switch blades and contactsin the following manner: Switch blade RSW'I is moved to engage contactRIC as shown in dotted line, while switch blade RSWZ moves from contactRIA to contact RIB as shown in dotted line thus breaking the circuit viaflame sense wire 90 between pilot control unit 84 and pilot assembly 40.

(8) The spark/flame rod 27 (see FIG. 4) is transferred from the flamesense input of the pilot control unit 84 to the secondary of the highvoltage transformer T1 by the operation of contacts RlA and RIB.

(9) When item 7 is complete, a voltage is applied through contact RIC tothe primary of T1. The high voltage is applied to the spark/flame rod 27through the contact R18.

(10) After a delay of 2 to 3 seconds the delay of TD is over and thecontact TD-l opens by moving the switch blade thereof as shown in dottedline, thus rcmoving the voltage from TD and R1. (ll) The switch bladesRSWI and RSWZ of R1 operate in the reverse order to that set forth initem 7, namely:

(a) R lC opens. (b) RIB opens. (c) RlA closes. (12) After the operationof item 11, the spark/flame rod is connected to the flame sense circuitof the pilot control unit 84.

If the pilot control unit 84 did not sense a flame, the operation isrepeated when the time delay (TD) cools down to a point where contactTD1 closes. It continues to ignite and sense until the delay of thepilot control unit is over. At this time the pilot control locks itselfout, removing voltage from the transfer unit input, closing the pilotgas valve 80 and remaining in this position until the interlock ismanually cleared after which the above operation will be repeated.

If the pilot control unit 84 did sense the presence of a flame in thepilot section, the voltage is immediately removed from the transfer unitinput. An operating voltage or signal is applied to the safety shutoffvalve allowing the gas to be directed to the manifold 48 of the burnerassembly.

As the temperature of the heated device approaches the set point of thecontroller, the valves 71 and 77 begin to position themselves therebyreducing the air and gas supplied to the burner assembly. These valveswill allow an amount of air and gas to be supplied to the burnerassembly to regulate and hold the temperature on the required set point.

If at any time the pilot control unit 84 fails to sense a flame, thesignal is immediately removed from the safety shutoff valve 75 and itimmediately closes. The voltage is again applied to the transfer unitinput and the pilot ignite/sense repeats. Again when the flame issensed, the operation of the safety shutoff valve 75 may be initiated.

It has thus been shown that the ignitor-burner assembly as illustratedby the FIGS. 1 and 4 embodiments has the following advantages: (1) itsoperation will not be affected by varying air and/or gas pressures, (2)it produces a high temperature, high velocity flame to produce easierand smoother ignition of a main burner, (3) it is immune to varyingenvironmental conditions, (4) the flame rod is protected in such amanner that it does not sufler the deleterious effects that plague theprior art units, (5) the air and gas mixing is accomplished in such amanner that it produces a mixture which is easily ignited and veryetficient, while eliminating flash back, (6) any gas pressure may beused with excellent results provided that the gas inlet be provided withorifice means at high pressures, and (7) any air pressure may be usedassuming that it provides an adequate amount of air to satisfy the ratioof air to gas.

While the ignitor-burner assembly has been illustrated as a pilotignitor for a main burner assembly, it is not intended to limit itsapplication to this area, and the ignitor-burner may be effectively usedin any application requiring a high temperature flame such as waterheating systems or steam generation systems by directing water throughappropriate tubing which is in contact with the flame of theignitor-burner.

While not shown, the ignitor-burner assembly of the invention may bemodified to provide eflicient burning of other mixtures such asoxygen-natural gas, oxygenhydrogen, oXygen-acetylene, air-hydrogen, andair-acetylene.

Although particular embodiments of the invention have been illustratedand described, modifications thereof will be readily apparent to thoseskilled in the art, and it is intended to cover in the appended claimsall such modifications as come within the true spirit and scope of theinvention.

What I claim is:

1. In combination With a combustion chamber, an ignitor assemblycomprising: air supply means, gas supply means, and ignition means; saidair supply means including means for providing -a supersonic air flow;said gas supply means including means for providing a subsonic gas flow;said air and gas supply means being constructed and arranged to providea homogeneous mixture thereof, said air supply means and said gas supplymeans being positioned in a concentric arrangement With respect to saidignition means.

2. The combination defined in claim 1 additionally including a flame rodassembly.

3. An ignitor-burner assembly comprising a combustion chamber, anignitor assembly, a flame rod and sensor assembly, a flame holder, meansfor supplying air and fuel to said combustion chamber, and means forsupplying fuel and air to said ignitor assembly; said ignitor assemblyincluding fuel manifold means, air manifold means, a plurality of fuelconduits operatively attached to said fuel manifold, a plurality of airconduits operatively attached to said air manifold, and ignition means,said fuel conduits being positioned intermediate said air conduits; saidignition means including positive and negative electrodes and b-afliemeans positioned a predetermined distance from one end of each of saidelectrodes; said fuel and air conduits being concentrically locatedaround said ignitor means and having the terminal ends thereof spacedfrom said baflie means of said ignition means.

4. The ignitor-burner assembly defined in claim 3, wherein said flamerod and sensor assembly is located in a spaced relationship to saidignitor assembly.

5. The ignitor-burner assembly defined in claim 3, wherein said flamerod and sensor assembly is incorporated into said ignitor assemblywhereby said positive electrode of said ignitor assembly functions asthe flame rod of said flame rod and sensor assembly.

6. The ignitor-burner assembly defined in claim 3, wherein said ends ofsaid electrodes and one end of said flame rod and sensor assembly extendthrough said flame holder, said flame holder additionally including aplurality of passageways therethrough.

7. A natural gas pilot burner comprising a housing, an ignitor assembly,a flame rod assembly, and a flame holder having passages therethroughand operatively mounted in said housing; said ignitor assembly includinggas and air manifolds, a plurality of conduit means havpredetermineddistance from one end of said electrode means, said one end of saidelectrode means extending through said flame holder, said gas and airconduit means being positioned concentrically with respect to saidignition means and having the other ends thereof terminating in a spacedrelationship with respect to said baifle means.

8. The natural gas pilot burner defined in claim 7, wherein said flamerod assembly includes a flame rod and insulating means for said flamerod, said flame rod having one end thereof extending through said flameholder.

9. The natural gas pilot burner defined in claim 8, wherein said flamerod is positioned in said ignition means of said ignitor assembly andadditionally functions as the positive electrode means of said ignitionmeans.

' 10. An ignitor comprising a gas manifold, an air manifold, ignitionmeans, a plurality of conduits operatively connected to said gasmanifold, a plurality of conduits operatively connected to said airmanifold, said conduits being coaxially aligned with said ignition meanswith said gas conduits being positioned substantially intermediate saidair conduits, said ignition means including positive and negativeelectrode means with insulation means therefor and baflie meanspositioned a predetermined distance from one end of said electrodes,said gas and air conduits terminating in a spaced relationship to saidbaffle means.

11. The ignitor defined in claim 10, wherein said gas manifold includesmeans for determining the flow of gas thereinto.

References Cited by the Examiner UNITED STATES PATENTS 1,647,675 11/1927Vedder 158109 X 2,402,763 6/1946 Tongini 158--115 2,784,553 3/1957 Corsoet a1. 6039.82 2,794,620 6/1957 Arnold et a1. 15827.4 2,970,178 1/1961Braconier et a1. 158-118 3,002,351 10/1961 Sloan 6039.82

FREDERICK KETTERER, Primary Examiner.

7. A NATURAL GAS PILOT BURNER COMPRISING A HOUSING, AN IGNITOR ASSEMBLY,A FLANGE ROD ASSEMBLY, AND A FLAME HOLDER HAVING PASSAGES THERETHROUGHAND OPERATIVELY MOUNTED IN SAID HOUSING; SAID IGNITOR ASSEMBLY INCLUDINGGAS AND AIR MANIFOLDS, A PLURALITY OF CONDUIT MEANS HAVING ONE ENDTHEREOF OPERATIVELY CONNECTED TO SAID GAS MANIFOLD, A PLURALITY OFCONDUIT MEANS HAVING ONE END THEREOF OPERATIVELY CONNECTED TO SAID AIRMANIFOLD, SAID GAS CONDUIT MEANS BEING POSITIONED INTERMEDIATE SAID AIRCONDUIT MEANS, IGNITION MEANS INCLUDING POSITIVE AND NEGATIVE ELECTRODEMEANS AND BAFFLE MEANS POSITIONED A PREDETERMINED DISTANCE FROM ONE ENDOF SAID ELECTRODE MEANS, SAID ONE END OF SAID ELECTRODE MEANS EXTENDINGTHROUGH SAID FLAME HOLDER, SAID GAS AND AIR CONDUIT MEANS BEINGPOSITIONED CONCENTRICALLY WITH RESPECT TO SAID IGNITION MEANS AND HAVINGTHE OTHER ENDS THEREOF TERMINATING IN A SPACED RELATIONSHIP WITH RESPECTTO SAID BAFFLE MEANS.